Dopamine (DA), norepinephrine (NE), and epinephrine (EPI) and their metabolites and dopamine-beta-hydroxylase (DBH) are present in human plasma and cerebrospinal; fluid (CSF). Levels of these substances reflect the balance between their release and removal. The increases in levels of NE and EPI with standing, exertion, stress, drugs, administration, etc., are used to examine sympathetic neuronal responsivity. The responses and level of activity of the sympathetic nervous system in cardiovascular disorders (hypertension, hypotension) a variety of psychiatric disorders, and after treatment with drugs are being examined.